In recent years, unconventional nonvolatile memory (NVM) devices, such as ferroelectric random access memory (FRAM) devices, resistive random access memory (RRAM) devices, and phase change random access memory (PCRAM) devices have emerged. In particular, PCRAM devices, which exhibit a switching behavior between a high resistance state and a low resistance state, have various advantages over conventional NVM devices. Such advantages include, for example, compatible fabrication steps with current complementary-metal-oxide-semiconductor (CMOS) technologies, low-cost fabrication, a compact structure, flexible scalability, fast switching, high integration density, etc.
Generally, a PCRAM device includes a top electrode (e.g., an anode) and a bottom electrode (e.g., a cathode) with a phase change material layer interposed therebetween. Further, the bottom electrode is coupled to the phase change material layer with a conductive structure, typically knows as a “heater” structure. To transition the PCRAM device to the low resistance state, which is typically referred to as a set operation, a relatively low electrical current signal is applied on the phase change material layer through the heater structure to anneal the phase change material layer at a temperature between respective crystallization (lower) and melting (higher) temperatures of the phase change material layer so as to crystallize the phase change material layer; and to transition the PCRAM device to the high resistance state, which is typically referred to as a reset operation, a relatively high electrical current signal is applied on the phase change material layer via the heater structure to anneal the phase change material layer at a temperature higher than the melting (higher) temperature of the phase change material layer so as to amorphorize the phase change material layer. In particular, a current level of the applied electrical current signal that can successfully amorphorize/crystallize the phase change material layer is proportional to a contact area size at an interface between the heater structure and the phase change material layer. For example, the bigger the contact area size is, the higher the current level of the applied electrical current signal needs to be.
The heater structures of existing PCRAM devices, however, couple respective phase change material layers with relatively large contact areas, which disadvantageously requires respective current levels to be relatively high. Various issues may accordingly occur in exiting PCRAM devices when applying such a high current level signal, for example, less reliability, higher power consumption, etc. Thus, existing PCRAM devices and methods to make the same are not entirely satisfactory.